Taking the free bus as they don't allow cars to go up anymore.
Can take the cable car too.
I will suggest reaching seoul tower around 1-2 hour before sunset so can take photos of seoul tower in day and go up before the sun stare to set. Will be able to catch the day and night scenery of seoul.
view from seoul tower..
I went in second week of novemeber in 2010 and 1st week of november in 2011. However, I manage to catch pretty maple leaves in 2010. In 2011, some of the maples leaves turned yellow or was dried up.
From Chungmuro Station (subway lines 3 & 4), use exit #2 and take bus #2(Yellow Bus) to N Seoul Tower (08:00 to 24:00 / every 8 min / 15 min travel time) Fee 550won